The present invention relates to an ignition interlock that positively identifies a principal operator and measures the blood-alcohol content directly from a bodypart of the operator. The interlock prevents operation of equipment in which it is installed.
Drunk driving has claimed about 250,000 lives in the past ten years. Every year drunk drivers injure over 650,000 people. Estimates for property damage and medical expenses exceed twenty four billion dollars annually. Statistic studies have shown that eighty two percent of first time drunk driving offenders are problem drinkers or alcoholics. Moreover, more than seventy percent of drivers with suspended licenses continue to drive without insurance.
To prevent convicted drunk drivers from continuing to drive while intoxicated, several law enforcement programs employ ignition interlocks that are installed in convicted drivers'vehicles to prevent the vehicles from being started while the driver is intoxicated. Known interlock devices connect breath-alcohol analyzers to a vehicle's ignition system.
Systems currently available include Ignition Interlock's LIFESAFER.TM. and Guardian Interlock System's GUARDIAN INTERLOCK.TM.. These devices include a handheld breath-alcohol analyzer and a data logger that records vehicle activities and test results and the time and date at which each took place. With either of these devices, a driver must pass a breath test by blowing into the device before starting the vehicle. Unless the driver passes the test, the vehicle will not start. The units also conduct tests at random intervals once the vehicle has been started to deter the driver from drinking after engine start and continuing to drive while intoxicated.
Both breathalyzers determine blood-alcohol concentration through a measurement of breath-alcohol concentration. They convert the breath reading by comparing the fraction of the amount of ethanol in the exhaled air with a partition ratio, which is the average ratio of the amount of ethanol in exhaled air to the level of ethanol in blood. This partition ratio is based on 2,100 ml of breath air containing the same weight of ethanol as 1 ml of blood.
Although the partition ratio represents the average, the ratio is not accurate for a large number of individuals. Thus, a disadvantage of breath-alcohol measurement is that significant number of individuals have normal breath-alcohol concentrations notably above or below the partition ratio. This often leads to erroneous determinations of blood-alcohol concentrations that might render false indications of intoxication or non-intoxication for drivers whose normal breath-alcohol levels differ from the average.
Another disadvantage stems from the effects of environmental factors on breathalyzers. Breath fresheners and medical inhalants, for example, contain alcohol. Although this alcohol is not in the blood, the breathalyzer detects it in the breath sample, and the use of fresheners of inhalants may cause unwarranted alcohol-test failures. Also, because breathalyzers determine ethanol content by measuring carbon content in the sample breath, dust, cigarette smoke, and fuel vapors can incorrectly result in the breathalyzer registering a failed alcohol-level test.
More accurate methods of determining blood-alcohol concentration involve spectroscopic blood analysis, such as disclosed in U.S. Pat. Nos. 5,515,847, 5,435,309, and 5,361,758. These approaches conduct a chemical analysis of a subjects blood by measuring light emerging from the subject's tissue, such as a finger. Most methods of spectroscopic analysis prescribe irradiating the subject with infrared light and measuring the light emerging from the other side of the tissue, although the '847 patent also discloses measuring infrared absorption patters from infrared emissions generated by the subject's body. Ignition interlock devices, however, have not been fitted with spectroscopic blood-alcohol analyzers.
A further concern in the operation of ignition interlock devices is that persons other than the driver may take and pass the alcohol concentration test, permitting a drunk driver to operate or continue operating the vehicle and defeating the preventive function of the interlock. To address this concern, the GUARDIAN.TM. requires a the subject to enter a code of breath pulses after passing a test. A person other than the driver may easily learn this code. As a result, the code requirement does not positively identify the test taker.
A different type of device known in the art for identifying individuals, which has not been employed in ignition interlock devices, electronically scans fingerprints. Such devices are taught, for example, in U.S. Pat. Nos. 5,546,471, 5,467,403, 5,088,817, and 5,067,162. Finger print imaging and recognition devices are sold by Biometric Identification, Inc. and Fingerprint technologies. In known devices, a subject places his or her finger against a light conducting platen. Light is then reflected off the fingertip, and an image of the reflected light is scanned. Image processing algorithms in a computer then compare the scanned image to a prerecorded fingerprint image. Depending on the degree of correlation between different regions of the two images, these images are either considered a match or not. Fingerprint identification software is sold, for instance, by East Shore Technologies, Inc.
An easy to use ignition interlock is needed for acquiring accurate blood-alcohol measurements that are not significantly affected by environmental factors or variable normal breath-alcohol levels. The needed interlock should also positively identify the test subject during the test, to prevent people other than the driver from taking the test.